Method of forming berylliumcopper alloy bellows



W. V. HOBBS Sept. 25, 1951 METHOD OF FORMING BERYLLIUM-COPPER ALLOY BELLOWS Original Filed March 12, 1943 2 Sheets-Sheet l m 7/ q /7 E M INVENTOR WALTER V. Hoses BY haw-1f ATTORNEY W. V. HOBBS Sept. 25, 1951 METHOD OF FORMING BERYLLIUM-COPPER ALLOY BELLOWS 2 Sheets-Sheet 2 Original Filed March 12, 1943 I R Y s E m /m EH .0 mv M WW Y Lr WAB Patented Sept. 25, 1951 METHOD OF FORMING BERYLLIUM- COPPER ALLOY BELLOWS Walter V. Hobbs, Delaware, Ohio, assignor to Ranco Incorporated, Columbus, Ohio, a corporation of Ohio Continuation of application Serial No. 478,984,

March 12, 1943.

This application September 25, 1947, Serial No. 776,104

1 Claim.

1 The present invention relates to the method of bonding an alloy, such as beryllium-copper with another metal or like alloy and, more particularly to forming a metallic pressure cell, such as an aneroid cell including a flexible resilient metal wall sealingly joined with the second metal wall. .The space between these walls is subit is an object of the present invention to heat the portions of the walls, which are to be joined,

and the fusible bonding metal at such high rate and temperature that the fusible bonding metal fuses before appreciable precipitation in the alloy wall or walls takes place.

In carrying out the above objects, it is a further objectof the present invention to provide a method of aging the flexible wall by heating the same to a temperature below the fusing temperature of the fusible bonding metal over a period sufficient to cause hardening of the 'alloy by precipitation of the gamma phase.

A further object of the present invention is to include in the method the plating of the walls of the cell with one of the constituents of the .alloy. More specifically, the method includes the plating of the wall with copper when the wall is formed of beryllium-copper.

Further objects and advantages of the present invention will be apparent from the, following description, reference being had to the accompanying drawings wherein a preferred form of embodiment of the invention is clearly shown.

In the drawings:

Fig. l is a side view showing two aneroid cells, in the form of metallic bellows, attached to one another;

Fig. 2 is a sectional view taken on .line 2-2 of Fig. 1, showing one of the bellows on a somewhat larger scale;

. Fig. 3 is a fragmentary sectional view of one of the bellows showing the solder in place prior to subjecting the solder to fusing temperature;

Fig. 4 is a fragmentary sectional view of the center or bellows connecting fitting and part of r the bellows wall, the view being on a larger scale and the thickness of the solder being exaggerated;

Fig. 5 is a. view partly in section of two bellows -,whi ch are to be joined withone another and .metal walls for the cell.

the center fitting, and showing the two electrodes employed for heating the fitting;

Fig. 6 is a fragmentary sectional view on a larger scale showing the center fitting for the bellows;

Fig. '7'is a fragmentary sectional view of one of the outer ends of the bellows, the closure fitting or plug'therefor, and the high frequency coil employed for inducing current into the plug; and

Fig. 8 is a side view of another form of bellows.

Although the present invention is not limited to the manufacture of thin wall flexible metallic bellows, bellows or pressure cells are shown and described as examples for illustrating the invention. When an aneroid cell, such as a metallic bellows, is employed, it is necessary to hermetically seal the same. It has been found that soft solder cannot be successfully employed for bonding the parts of. the cell when the cell is to be used as a pressure responsive element in a sensiti-ve controller. One of the reasons for this is the hysteresis loss and creeping inherent in the soft solder. It is therefore necessary to employ a hard solder to minimize hysteresis loss and creeping Of the fibers of the metal. The difficulty encountered in employing a hard solder is that the fusing, point of such solder is atsuch high value, that precipitation in the alloy of the cell walls occurs when the walls are heated to solder fusing temperature. This is particularly true. when beryllium-copper is utilized at the The beryllium-copper alloy sheets,,from which these cell walls are formed, comprise approximately 97.75% copper, 25% cobalt and 2% beryllium, the beryllium forming with the copper an a-solid solution, i. e., atnormal temperatures, precipitation issubstantially nil, atleast for ordinary periods of time, but, if subjected to high temperatures, such-as that necessary to fuse'relatively hard solder, precipitation of the 'y-phase is accelerated and if subjected to still higher temperatures, necessary to fuse still relatively harder solders, precipitation of the B-phase occurs.

It is necessaryto heat treat the beryllium copper at'a'temperature and for a time to effect sumcient precipitation of the y-phase so that the proper resiliency, tensil strength and other characteristics desirable are imparted to the metal walls of the cells.

It has been found that, when hard solder is used, the precipitation of 'the 6-phase during the soldering phase'was such that the walls of the cellv becametoo brittle and cracked when 3 subjected to the strains to which the cell was subjected. Also, the tensil strength of the walls was less than that desired. It has also been found that the solder tends to penetrate between the crystalline structure of the cell walls which also is detrimental to the performance and the life of the cell. These deficiencies were particularly the case when the beryllium-copper cell was bonded to relatively large or massive end fittings or plugs and this was due to the length of time that heat had to be applied to heat the mass of the fittings to solder fusing temperature.

It has been discovered that the parts forming the cell walls and fittings can be soldered to one another with no precipitation or with such slight precipitation as not to detrimentally affect the characteristics of the metal. It has been discovered that the beryllium-copper can be heated to a temperature above the fusing temperature of the hard solder and for a period sufficient to fuse the solder with no appreciable precipitation taking place. This has been accomplished by bringing the temperature of the beryllium-copper to above the fusing point of the solder quickly and maintaining this high temperature for a limited time only, sufficient however to fuse the solder and permit the same to flow where desired.

Very satisfactory results can be obtained by subjecting the parts to be heated to a salt bath, or a furnace, or to heating one of the elements to be joined by a high frequency alternating current or by interposing one of the elements to be joined in the path of a low voltage and high amperage current, in which latter case, the element functions as a high resistance element in the circuit.

For a more general comprehension of the present invention, reference is made to the accompanying drawings in which in Fig. 1 two aneroid cells and 2| are shown. These cells are attached to one another by a center fitting or connecting plug 23 and the opposite ends of the cells are connected by fittings or plugs 24 and 25. Each of these cells is formed of a plurality of discs 26 and 21. Referring to Fig. 2, each of these discs 26 includes a circular peripheral flange 28 extending from one side of the disc and an inner circular flange 29 extending from the opposite side of the disc. Flange 29 defines a central opening 38. Disc 21 is also provided with a circular peripheral flange 3| extending from one side of the disc and an inner circular flange 32 extending from the opposite side of the disc. Flange 32 defines a central opening 33. The disc 26 is somewhat larger in diameter than the disc 21 so that the flange 3| can telescope within the flange 28. The opening 33 in the disc 21 is slightly larger than the outside diameter of the flange section 29 so that the flange 29 can telescope within the opening in the disc 21. The discs are each provided with circular concentric corrugations 35.

In the manufacture of the bellows, the discs 26 and 21 which are formed of beryllium-copper are preferably plated either by flash plating the sheets prior to formation of the discs or by flash plating the discs themselves so that a thin coating of copper covers the beryllium-copper alloy. Then taking one of each of the discs 26 and 21, a ribbon 31 of hard solder of approximately .004

inch thickness is forced between the outside of the flange 3| and the inside of flange 28. A ring of hard solder 38 is placed about the flange 32. A series of these sub-assemblies, each including a disc 26, a disc 21, a solder ribbon 31 and a solder ring 38, are stacked; each of flanges 29 of a subassembly telescopes within the opening 33 defined by the next adjacent flange 32 of the next adjacent sub-assembly. These sub-assemblies when so stacked may be considered as an assembly which is then subjected to heat for melting-the solders' 31 and 38. A preferred manner of heating this assembly is to convey the same through a furnace containing a reducing atmosphere. Preferably, a percentage of hydrogen is employed in the atmosphere in the furnace to prevent oxidation of the beryllium-copper during the heating and cooling periods. In the present invention, the solder employed consists of silver 50%, copper 15 /2 zinc 16 and cadmium 18%. This solder is made in accordance with United States Patent No. 1,899,701. This solder fuses and flows at a temperature between 635 C. and 640 C. The assembly is subjected to from 650 C. to 675 C. for a period of approximately forty-five seconds and is then immediately cooled, preferably by cooled reducing atmosphere. During this brief heating eriod, the solder 31 fuses. Likewise, the solder ring 38 fuses and by capillarity flows upwardly between the flanges 29 and 32. Preferably the discs 26 and 21 are formed of .008 inch sheet metal and are shown grossly exaggerated in the drawings. Likewise, the solder at the joints is grossly exaggerated in some of the views.

Next the bellows, formed by the joined or bonded discs, are connected with one another by the center fitting or plug 23. This fitting is provided at opposite ends with circular bosses 42 and 43 having solder ring holding grooves 44. A ring of solder 45 is placed in each of these grooves and the bosses 42 and 43 are telescoped within the openings 33 formed by the flanges 32. Electrodes 46 and 41, diagrammatically shown in Fig. 5, are extended through the bellows and engage the ends of the bosses 42 and 43. The connector 23 forms a part of the electric circuit and this circuit is in the order of slightly less than one volt and of an amperage between six thousand and eight thousand. This connector 23 may be formed of copper, brass or other alloy and in the present case is formed of brass; the resistance thereof to this current is suflicient to generate heat of such value as to cause the fusing and the flowing of the solder rings 45 within ten to fifteen seconds. The current is then removed and the solder solidifies immediately. Immediately thereafter, the joined bellows are then quenched in water at room temperature or at a somewhat higher temperature. The application of heat to the beryllium-copper of the bellows is insufficient to cause appreciable precipitation of the gamma phase.

A preferred method of bonding the outer plugs 24 and 25 is more or less diagrammatically shown in Fig. 7. This plug is provided with a hollow section 49, a peripheral groove 50 adapted to contain a solder ring 5| and an outwardly extending boss 52. This plug 24 with the solder ring 5| is inserted within the opening 30 in flange 29. The boss 52 is extended within a high frequency coil 54 of the order of two hundred volts and a frequency of four hundred thousand cycles per second. Coil 54 comprises substantially one turn of metal tube and is hollow as shown at 55 to provide a path for a cooling liquid. Suflicient heat is generated in the plug 24 within ten to fifteen seconds. by induced current from coil 54, to cause fusing and flowing of the solder 5|. The bellows assembly and plug 24 is then removed from the influence of the coil 54 and after the solder solidifies, the assembly is then quenched in water at room temperature or slightly above room temperature. The other plug 25 is then soldered in place in the same manner. If it is desirable to connect the interior of the bellows with a tube such as tube 55, this can be accomplished by drilling a hole 57 through side wall of the plug 24 or 25 and inserting the tube 56 into the same. This tube is preferably soldered in place at the time that the plug is joined to the bellows. Preferably a coil of solder 59 is wound about the exterior of the tube 56 and placed adjacent the opening 51.

It is to be understood in the present embodiment the silver-copper-zinc-cadmium solder, as hereinbefore described, is employed at all soldered joints. It has been discovered that a temperature of 650 C. can be maintained for as long as two minutes without structural injury to the beryllium-copper, i. e., the precipitation of the gamma phase is unappreciable and likewise the solder penetration between the grain crystals is not detrimental. Also, it has been discovered that when heat is applied at a temperature of 675 C. up to one minute, no structural injury is imparted to the beryllium-copper and highly desirable results can also be obtained at 700 C. for a period of fifteen seconds. In view of the fact that the time element is too critical between temperatures 675 C. and 700 C. and in view of the fact that solder melts at 635 C. to 650 0., it has been found most practical to employ temperatures between 650 C. and 675 C. at which temperature the time element is not so critical.

The longer time period is particularly more desirable when a furnace is employed by reason of the fact that the heat is applied more indirectly and at a slower rate to the bellows.

Also in the preferred method, as has been stated above the beryllium-copper is copper plated by either flash plating the sheets or the discs prior to the soldering operation. In this manner the beryllium, which normally tends to oxidize on the surface of the disc during the heating thereof, will be completely absorbed in the copper plating. Thus, the surface of the discs is free of oxide and, therefore, presents an excellent surface to the flow and adherence of the silver solder.

The electrical methods of heating as herein described are particularly advantageous when relatively massive fittings are required. When the fitting is a small mass such as that shown in Fig. 8, the fitting or fittings may be attached to a stack of discs and soldered in place in the furnace at the same time that the inner flanges and outer flanges of the discs are soldered, respectively, to one another. It will, of course, be understood that these plugs or fittings will each be provided with a circumferential groove and a solder ring similar to that shown at 44 and 45, respectively in Fig. 6. However, if the fittings are relatively large, the time interval necessary to bring this mass up to solder fusing temperature would, in some instances, be suflicient to cause excessive precipitation of the beryllium and excessive penetration of the solder between the grain crystals of the beryllium-copper. By employing the electrical methods of attaching the fittings, the flanges of the discs are heated by conduction from the fittings and the time interval necessary for fusing the solder is so short that no part of the discs except the inner flange being bonded is reheated to the fusing temperature of the solder and this in spite of the fact that the discs are excellent conductors of heat. In this electrical heating method, the precipitation of the gamma phase is maintained at a minimum.

While the forms of embodiment of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claim which follows.

This application is a continuation of my copending application Serial No. 478,984 filed March 12, 1943, now abandoned.

I claim:

The method of forming a flexible berylliumcopper alloy wall device sealingly joined to a second wall which comprises first plating the walls with copper; then bonding an edge portion of the beryllium-copper alloy wall device with the second wall by a fusible metal having a fusing temperature above the temperature at which rapid phase change in the alloy would take place if the alloy were subjected to prolonged heating at such rapid phase change temperature, which bonding step consists in placing the portions of the wall device and wall to be joined adjacent to each other and disposing the fusible metal adjacent said portions, heating said portions and fusible metal at such high rate and temperature that the fusible metal fuses before an appreciable change in the alloy from the alpha phase occurs, and then cooling the wall device, wall and fused metal quickly; and then aging the assembly by heating the same to a temperature below the fusing temperature of the fusible metal for a period sufficient to cause hardening of the beryllium-copper alloy wall device by precipitation.

WALTER V. HOBBS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,433,213 Lowell Oct. 24, 1922 1,575,994 Laise Mar. 9, 1926 1,651,891 Hodges Dec. 6, 1927 1,944,106 Ragsdale Jan. 14, 1934 2,154,273 Kollsman Jan. 26, 1940 2,223,312 Briggs Nov. 26, 1940 2,237,309 McMinn Apr. 8, 1941 2,279,854 Whitney Apr. 14, 1942 2,296,435 Giard Sept. 22, 1942 2,326,022 Everett Aug. 3, 1943 2,330,943 Anderson Oct. 5, 1943 2,385,595 Woitscheck Sept. 25, 1945 FOREIGN PATENTS Number Country Date 712,693 France Aug. 20, 1934 OTHER REFERENCES Age Hardening of Metals, 1940, American Society for Metals, Cleveland, Ohio, pages 10 and 11. Sil-fos and Easy-Flo Bulletin No. 12, page 13. 

